Reference Libraries

Geared towards adding FHIR capability to existing applications (e.g. it's not a database, it's a library for quickly bolting FHIR on to your own database, or connecting to other FHIR servers as a client)

Supports all resource types, most operations, and both xml and json encodings

Other Open source Implementations

FHIRBase - open source relational storage for FHIR with document API based on PostgreSQL. FHIRBase is an attempt to take the best parts of Relational & Document Databases for persistence of FHIR resources. FHIRBase stores resources relationally and gives you the power of SQL for querying & aggregating. At the same time FHIRBase provides a set of SQL procedures & views to persist and retrieve resources as a json documents in one hop.

the FHIR build tool itself is open source and includes various definitional and reasoning tools. See [1]. If you aren't signed up to the HL7 GForge, you can access the FHIR repository at [2] anonymously.

JSON-to-XML-Converter - JavaScript based open source library to convert FHIR between JSON and XML. It is built from the FHIR XML Schema.